Optimal Coordination of DOCRs Considering Transient States of Fault Current in Interconnected DG Systems using User-Defined Dynamic Model of Relays

Abstract

In real networks, short circuit (SC) current doesn't have a fixed value but it has time variable values. So that, to avoid possible miss-coordination between directional overcurrent relays (DOCRs), transient states of fault current must be considered during coordination. In this paper, a user-defined dynamic model of DOCRs - optimally select the relays four parameters (time multiplying setting (TMS), pickup current (I_P) and constant coefficients (? and ?)) - is presented to consider the transient states of SC current - from both the utility and synchronous based distributed generators (DGs)- in coordination problem. The coordination problem is solved by three techniques; two hybrid meta-heuristic techniques: gravitational search algorithm- sequential quadratic programming (GSASQP) and particle swarm optimization- gravitational search algorithm (PSOGSA) and one mathematical method: find minimum constraints (FIMINCON). Each one of the presented techniques is applied to three different test systems- IEEE 3, 9 and 14 bus systems- in four different models for each system- to show the efficiency of the proposed user-defined dynamic model technique. Each system four models are (model 1: conventional steady-state model, model 2: user-defined steady-state model, model 3: Conventional dynamic model considering transient and model 4: proposed method (user-defined dynamic model considering transient). The results show a superiority of the meta-heuristic techniques over the mathematical method also show that the presented user-defined dynamic model technique is the most efficient method for DOCRs coordination in presence of transient fault. MATLAP program is used to obtain the transient SC current and to apply the proposed techniques.